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  • SCR based Car Ignition Code Lock

  • Created: Apr 19, 2016

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Summary

The circuit design is based on a simple design of code-lock system using micro switches and SCR for car ignition. The reference design uses S4N1RP from Littlefuse Inc., with ratings of 1 A to 70 A and 200 V to 1000 V, with gate sensitivities from 10 mA to 50 mA and 10 micro switches bank.


The functionality of the circuit starts when the user presses the correct switches in an orderly manner. The SCR1 that connected to switch 9 should be the first one to be press. The SCR1 will start to conduct and will start also to latch, also the anode of the SCR2 is connected to the cathode of SCR1, thus biasing SCR2 and now ready for conduction. When switch 3 is press, SCR2 will conduct and will biased SCR3. By the time switch 7 is press, SCR3 will conduct and RL1 will be active and will connect the line for ignition. There are 84 possible combinations using the switches, which only one combination can trigger the relay and connect it to the ignition. The other remaining switches are connected to the positive rail and directly to ground via R1.


The reference design can also be used in other application like door lock, or any other applications that used combination of keys. The design can also be improved by adding LEDs to indicate the system’s status. Alarms like siren or buzzer can be added to the design to indicate an incorrect key or switches combination and alarm the user.



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